The present invention relates generally to an anticipating dual set-point bistable thermostat.
Dual set-point thermostats commonly are manually programmed: the user selects the temperatures desired during operational normal and standby periods. In selecting the time to end the standby period, the user typically advances the setting to allow for temperature to readjust before being occupied. The disadvantage with such a situation is that the proper advancement varies with the thermal loading; sometimes the economical standby period is abandoned prematurely, while at other times the user reoccupies the space before it has completed its readjustment.
This problem is addressed in automated industrial "Energy Management Control Systems" (EMCS). Most EMCS's have provisions for automated dual set-point timing. These systems compute an estimate of the time required to return a zone from standby to operational temperatures using an array of meterological and environmental measurements, such as the outside wind speed, temperature, solar radiation, temperature of adjacent interior zones, etc. The disadvantages of this approach to automating dual set-point timing is the capital expense of the array of measurement instrumentation, the complexity and consequential expense of integrating the instrumentation to the EMCS, and the operational expense of calibrating and maintaining it.
U.S. Pat. No. 4,333,316 to Stamp et al discloses microprocessor based control apparatus for a heat pump system, which includes a standby mode having an expanded operating temperature range. U.S. Pat. Nos. 4,645,908 and 4,685,307 to Jones relate to energy management system for residential heating and cooling, for limiting electrical usage during peak times. U.S. Pat. No. 4,799,176 to Cacciatore discloses a programmable electronic digital thermostat which provides improved control of a temperature conditioning system for varying load conditions in order to maintain the ambient temperature within a predefined range of a scheduled set temperature while minimizing ambient temperature overshoots and undershoots. U.S. Pat. No. 4,298,946 to Hartsell discloses a programmable thermostat for maintaining desired temperatures during selected time periods and includes programmed instructions for measuring actual time rate of change of the ambient temperature during heating and cooling cycles to anticipate reaching the desired temperature. U.S. Pat. No. 4,388,692 to Jones discloses a similar thermostat further including programmed instructions for varying a threshold hysteresis temperature with time in discrete steps around the desired ambient temperature or set temperature. U.S. Pat. No. 4,442,972 to Sahay discloses a thermostat which includes programmed instructions for determining a restart time prior to the next scheduled time interval for initiating operation of the temperature conditioning system to achieve the next temperature at the scheduled time.